DE102007004813B4 - Method for producing a piezoceramic multilayer actuator - Google Patents

Abstract

According to various production methods for producing a piezoceramic multilayer actuator, in the course of the production method, multilayer locks (10) are electrochemically or mechanically processed in such a way that a recess structure is obtained. The lateral surfaces (22; 24) of the electrodes (20) inside these recesses are electrically insulated using the slip casting method in order to be able to contact the remaining electrodes by imprinting an outer metallization.

Description

The present invention relates to a method for producing a piezoceramic multilayer actuator.

Based on the piezoelectric effect, piezoelectric ceramics of suitable crystal structure can expand or contract in their interior when an electric field is generated. This change in length takes place with almost no delay relative to the controlling electrical signal and is also precisely controllable. Therefore, piezoelectric multilayer actuators are used as adjusting elements.

Since the controlling electric field strength in such multilayer actuators is in the region of several kV / mm, but moderate drive voltages are required in practice when using the multilayer actuators, the piezoceramic multilayer actuators are produced with layer thicknesses in the range of 100 μm. Typical manufacturing processes are slip casting or dry pressing. The individual ceramic layers are metallized and stacked on top of each other so that internal electrodes of opposite polarity can produce the piezoelectric effect between two ceramic layers. About an outer metallization parallel to the stacking direction or longitudinal axis of the piezoceramic multilayer actuator mutually all internal electrodes of the same electrical potential are electrically driven. In order that the internal electrodes of the respectively opposite electrical potential are not short-circuited, they are arranged offset in relation to the other electrodes in the area of the external metallization of the internal electrodes of the respective opposite potential. This layer structure within the piezoceramic multilayer actuator results in design-induced piezoelectrically inactive zones. Since the piezoceramic multilayer actuator expands or contracts in length only in piezoelectric active regions, since the internal electrodes of different polarity are arranged directly above one another in these regions, mechanical stresses occur within the multilayer actuator in the transition region to piezoelectrically inactive zones. These mechanical stresses led to crack formation in the layer structure of the multilayer actuator, which can impair the electrical contact of the outer metallization to the individual electrodes or even lead to total failure of the multilayer actuator. The problem of cracking is reduced by the use of fully active piezoelectric multilayer actuators. In these fully active multilayer piezoelectric actuators no piezoelectrically inactive or passive regions are present, because the inner electrodes of both electrical potentials extend on all sides over the entire cross section of the multilayer actuator up to its edge.

EP 1 206 804 B1 discloses a manufacturing method for piezoelectric multilayer actuators. On the individual multilayer structures electrochemically electrically conductive materials are deposited on the side surfaces of the electrodes of the same polarity. These materials form webs which are electrically connected to each other after insulating the side surfaces of the electrodes disposed between these webs.

DE 42 24 284 A1 discloses the production of a multilayer bar and its subsequent sintering as a precursor for the production of piezoceramic multilayer actuators. Such a bar has, for example, the depth perpendicular and the length parallel to its stacking direction according to a later multilayer actuator. Its width perpendicular to the stacking direction is a multiple of a later width of a piezoceramic multilayer actuator. After sintering, the electrode structure of the individual piezoceramic multilayer actuators is generated jointly on the multilayer bar and subsequently this is decomposed into individual multilayer actuators. To produce the electrode structure, electrochemically conductive material is deposited on the side surfaces of each second electrode. The intermediate regions, ie ceramic and electrode, are reset by etching or mechanical removal into the sintered multi-layer bar. These operations are expensive because the sintered multilayer bar is resistant to mechanical and chemical attack. Subsequently, an insulation layer is applied in the recessed areas and generates external electrodes for each subsequent multilayer actuator. Finally, the sintered multilayer bar is divided into individual piezoceramic multilayer actuators.

US 5 568 679 A and WO 2005/075113 A1 also describes the production of structured outer electrodes on an already sintered multilayer preform. At each inner electrode of the same polarity, an electrically insulating material is electrochemically deposited, so that the side surfaces of these electrodes are insulated to the outside. Subsequently, an electrically conductive material is applied to the outer sides, which connects the still exposed side surfaces of the electrodes of the other polarity. Finally, the sintered multi-layer bar with a structured electrode is divided into individual piezoceramic multilayer actuators.

DE 10 2006 001 656 A1 relates to a piezoelectric actuator and a method for producing the same with the following method steps: Provision a multi-layered, piezoelectrically active piezor comprising an alternating sequence of piezoelectric material layers and electrically conductive electrodes, wherein the internal electrodes each have at least one section led out to an associated surface region of the piezoelectric piezoelectric element; and selectively etching back at least a portion of the at least one portions of predetermined internal electrodes led out to the respective associated surface region of the piezoelectric piezoelectric element into the interior of the piezoelectric element by means of an electrochemical etching process to form a piezoactuator having defined recessed depression sections.

DE 10 2004 012 033 A1 describes a laminated piezoelectric element having a ceramic laminate formed by alternately laminating a plurality of piezoelectric layers and a plurality of internal electrode layers. A side surface provided with the first side surface electrode is further provided with first recessed groove portions contacting the ends of the second internal electrodes in the bottom portions thereof, and a side surface provided with the second side surface electrode is further provided with second recessed groove portions forming the ends of the second side electrodes first internal electrodes in the bottom areas brings into contact. The first recessed groove portions and the second recessed groove portions are filled with an insulating filler having an electrically insulating property so as to cover the ends of the second internal electrodes and the ends of the first internal electrodes. The insulating filler includes an insulating resin having an electrical insulating property and inorganic particles of an inorganic material contained in the insulating resin.

It is the object of the present invention to provide a manufacturing method for a piezoceramic multilayer actuator, which is feasible with less effort and therefore with lower costs compared to the prior art.

The above object is achieved by a manufacturing method according to independent claim 1. Advantageous embodiments and further developments of the present invention will become apparent from the following description, the drawings and the dependent claims.

The manufacturing method according to the invention comprises the following steps: producing a multi-layer bar as green body consisting of an alternating arrangement of a plurality of piezoceramic layers and a plurality of electrodes in a stacking direction of the multilayer bar, while a depth of the multilayer bar perpendicular to the stacking direction of a depth a multilayer actuator and a width of the multilayer bar perpendicular to the stacking direction corresponds to a width of a plurality of multilayer actuators and the electrodes extend over the entire depth of the multilayer bar, so that all side surfaces of the electrodes each up to the surface of broad sides of the multilayer bar range, and wherein the electrodes alternately extend on opposite end faces of the multilayer bar starting over not the full width of the multilayer bar, arranging opposite auxiliary electrodes to the around the porridge te of the multilayer bar, arranging opposing auxiliary electrodes at the spaced by the width of the multilayer bar end faces, so that with the opposite auxiliary electrodes around one electrode in the stacking direction each second electrode is electrically driven, electrochemical reset parallel to the depth of the multilayer -Riegel, in particular etching, a side surface of each second electrode, so that at opposite broad sides of the multilayer bar every other side surface of the electrode is set back into the multilayer bar and the recessed side surfaces of the electrodes on opposite broad sides of the multilayer bar in the stacking direction a piezoceramic layer are spaced from each other, coating the recessed side surfaces of the electrodes with an electrically insulating layer, and applying a plurality of external electrodes to the opposite one n broad sides of the multilayer bar parallel to the stacking direction, sintering and separating the multilayer bar parallel to its depth and stacking direction in a plurality of piezoceramic multilayer actuators, wherein after sintering the end faces are separated with the auxiliary electrodes such that no piezoelectrically inactive areas in the multilayer Stay behind.

In order to reduce the production cost of fully active piezoelectric multilayer actuators, most of the manufacturing steps are performed on a multi-layer bar in the green state. This bar is due to its not yet sintered ceramic structure with less effort and therefore editable at a lower cost. In addition, the multi-layer bar with auxiliary electrodes at its width-spaced end faces offers the possibility of simultaneously producing a plurality of piezoelectric multilayer actuators by separating the multilayer bar into individual multilayer actuators at the end of the manufacturing process.

To produce structured electrodes on the outsides of the multilayer bar first reset the side surfaces of each second electrode by etching in the multilayer bar or put into it. The forming recesses, in which the side surfaces of each second electrode are arranged, are filled with slip of an electrically insulating material after burnout. These materials are for example glass or ceramic. Based on the etching and the subsequent electrical isolation by slurry, the side surfaces of each second electrode to be electrically connected are exposed outside the valleys, so that they can be electrically connected to each other, for example, by printing an outer metallization.

According to a production alternative not according to the invention, instead of the electrochemical reset discussed above, an electrochemical deposition of electrically conductive material may take place on one side surface of each second electrode so that each second side surface of the electrodes protrudes from the multilayer latch at opposite broad sides of the multilayer bar, the protruding side surfaces of the electrodes on opposite broad sides of the multilayer bar in the stacking direction about a piezoceramic layer are spaced from each other and formed between the protruding side surfaces of the electrode depressions.

In the same way as described above, these depressions are filled with a slip of electrically-insulating material after burning out. Therefore, only the increased by electrochemical deposition side surfaces of the electrodes of the multilayer bar are free on its broad sides. In this method, too, the advantages of easier processing of a multi-layer bar in the green state and the simultaneous production of a plurality of multilayer actuators with the aid of this multilayer bar are utilized. Furthermore, it has an advantageous effect that the side surfaces of the electrodes to be electrically insulated which are arranged in depressions can be effectively insulated by means of slip. In addition, the burnout of the slurry takes place, for example, in combination with the sintering of the multilayer bar in order to achieve a further optimization of the production process.

According to a further non-inventive alternative of the manufacturing method for a piezoceramic multilayer actuator, the following steps are carried out: producing a multi-layer bar as a green body consisting of an alternating arrangement of a plurality of piezoceramic layers and a plurality of electrodes in a stacking direction of the multilayer bar while a Depth of the multilayer bar perpendicular to the stacking direction of a depth of a multilayer actuator and a width of the multilayer bar perpendicular to the stacking direction corresponds to a width of a plurality of multilayer actuators and the electrodes extend over the entire depth and width of the multilayer bar, or producing a piezoelectrically fully active Stacks consisting of an alternating arrangement of a plurality of piezoceramic layers and a plurality of electrodes in a stacking direction, removing a respective side surface of each second electrode parallel to the depth direction of the multi-layer bar by means of sawing, grinding, laser, erosion and / or pushing, so that at opposite broad sides of the multilayer bar each second side surface of the electrodes is set back into the multilayer bar and the recessed side surfaces of the electrodes at opposite Broad sides of the multilayer bar in the stacking direction are spaced apart around a piezoceramic layer, coating the recessed side surfaces of the electrodes with an electrically insulating layer and applying a plurality of outer electrodes on the opposite broad sides of the multilayer bar parallel to the stacking direction, sintering and separating the multilayer Parallel to its depth and stacking direction in a plurality of piezoceramic multilayer actuators.

The present invention will be described in detail with reference to the accompanying drawings. Show it:

1A , B different embodiments of a multilayer bar,

2 a schematic representation of the electrochemical treatment of a multilayer bar,

3 an enlarged detail of the multilayer bar after the non-inventive step of the electrochemical deposition,

4 a section of the multilayer bar after the process of etching,

5 an enlarged detail of the multi-layer bar to illustrate the non-inventive removal by means of sawing, grinding and similar methods,

6 a representation of the section along the line AA 5 .

7 an enlarged detail of the multi-layer bar to illustrate the non-inventive removal not parallel to the side surface of the electrodes,

8th a sectional view taken along the line AA 7 .

9 a sectional view taken along the line BB 7 .

10 a sectional view taken along the line CC 7 , and

11 a flowchart for schematically illustrating various procedures of the manufacturing process.

To produce the piezoceramic multilayer actuator, first piezoceramic green sheets are cast. Subsequently, the green sheets are printed with electrode material, which consists for example of silver-palladium alloys. These surfaces form the later internal electrodes 20 , Furthermore, the printed green sheets are arranged one above the other in the stacking direction S to form a stack. Preferably, an unprinted green sheet is arranged between two printed green sheets in order to reduce the risk of electrical short circuits in the interior of the later multilayer actuator.

After stacking the green sheets, these are present as a block, d. H. The width and depth of the block are each a multiple of the depth and width of a later multilayer actuator. In the green state, the block is sufficiently stable to be processed chemically, mechanically or otherwise. In addition, the structure of the block is less resistant than in the sintered state, so that a machining of the block with less effort is feasible.

The green state block (not shown) becomes a plurality of multilayer bars 10 divided, for example by sawing. The multi-layer bar 10 as a green body comprises an alternating arrangement of a plurality of piezoceramic layers 30 and a plurality of electrodes 20 in the stacking direction S. A depth T of the multilayer bar 10 perpendicular to its stacking direction S corresponds to a depth of a multilayer actuator after manufacture and a width B of the multilayer bar 10 perpendicular to its stacking direction S corresponds to a width of a plurality of multilayer actuators after their production (see. 1A , B). The electrodes 20 of the multi-layer tie 10 extend over the entire depth T of the multilayer bar 10 ,

According to one embodiment (cf. 1A ) corresponds to the height H of the multilayer bar 10 approximately at a height of a later multilayer actuator in the sintered state. After further processing steps and sintering (see below), the multi-layer bar becomes 10 divided into individual multilayer actuators by separating cuts parallel to its stacking direction S (see the dashed lines in FIG 1A ). According to another embodiment (cf. 1B ) becomes the sintered multi-layer bar 10 divided by cuts parallel and perpendicular to its stacking direction S along the dashed lines. With the help of the multi-layer tie 10 In the green state, a plurality of multilayer actuators are thus simultaneously produced, while also a simplified processing in the green state is utilized within the scope of the production method.

The multi-layer bar 10 in the green state comprises the already mentioned above, each arranged alternately in the stacking direction S piezoceramic layers 30 and electrodes 20 , The side surfaces 22 . 24 the electrodes 20 each extend to the surface of the broadsides 12 of the multi-layer tie 10 , The multi-layer bar 10 includes at its opposite end faces 15 one auxiliary electrode each 25 , Every second electrode 20 begins at an auxiliary electrode 25 and ends in front of the opposite auxiliary electrode 25 , The electrodes 20 therefore do not extend over the entire width B of the multilayer bar 10 , Every second electrode 20 with the side surfaces 22 or 24 is thus based on the use of the auxiliary electrodes 25 electrically controllable together. However, this construction also results in the piezoelectrically inactive regions 5 adjacent to the front ends 15 of the multi-layer tie 10 , These are to be regarded as lost areas for the production of multilayer actuators, as they have no further benefit after completion of the manufacturing process.

After the multi-layer bar 10 is present in the green state, ie the steps of producing the multilayer bar S1 and arranging auxiliary electrodes S2 are completed, preferably becomes a broadside 12 insulated with a passivation layer. After application of the passivation layer, the multilayer bar is formed 10 electrochemically treated in an electrolyte bath (cf. 2 ). It is also conceivable to process the multilayer bar without passivation layer. In this case, only one broadside 12 of the multilayer bar into an electrolyte 52 (see. 2 ) immersed to process this broadside electrochemically.

With the help of in 2 illustrated, not according to the invention, plating is the multilayer bar 10 Electrochemically processed by electrically conductive material on the side surfaces 22 ; 24 the electrodes 20 is deposited. These materials include gold, a silver-palladium composition, or other metals and alloys that will survive subsequent thermal treatment without damage.

The plating bath contains the electrolyte 52 and a plating electrode 54 for applying a DC electrical voltage over the voltage source 50 between the plating electrode 54 and one of the auxiliary electrodes 25 , The DC voltage source 50 Only to one of the auxiliary electrodes 25 connected, so on a broadside 12 only the side surfaces 22 be coated with electrically conductive material. During coating, the metal ions migrate out of the electrolyte 52 in the electric field in the direction of the electrodes 20 and divide there on the side surfaces 22 from. After the deposition process, the passivation layer is removed and on the opposite broad side 12 applied or it will be the opposite broadside 12 immersed in the galvanizable. Because now the other auxiliary electrode 25 with the DC voltage source 50 is connected to the opposite broadside 12 only the side surfaces 24 the electrodes 20 coated with electrically conductive material.

The coated side surfaces 22 . 24 on the opposite broad sides 12 are therefore each a piezoceramic layer 30 spaced apart as in 3 is shown. The electrochemically deposited electrically conductive material on the side surfaces 22 or 24 the electrodes 20 thus closes sinks 40 one in which one electrode each 20 is arranged.

According to a production alternative of the invention, a similar sink structure as in FIG 3 produced by electrolytic etching S4. For this purpose, the multi-layer bar 10 only with a broadside 12 or completely with a previously passivated broadside 12 immersed in an etching bath. The etching bath preferably comprises conventional electrolyte solutions, such as, for example, aqueous sodium chloride solution or sodium nitrate solution. Thereafter, via only one auxiliary electrode 25 a DC electrical voltage to the electrode 20 with the side surfaces 22 created. Therefore, only the side surfaces 22 the electrodes 20 electrochemically removed. After that, the opposite broadside 12 immersed in the etching bath and the other auxiliary electrode 25 electrically controlled. This will make the side surfaces 24 the electrodes 20 ablated. It is also conceivable, the opposite broadside 12 to be provided with a passivation layer and the other auxiliary electrode 25 to drive electrically. With the help of this etching process, the side surfaces 24 etched away or reset. It forms again on both broadsides 12 a plurality of sinks 40 between each non-etched side surfaces 22 or 24 the electrodes 20 out. Because the side surfaces 22 . 24 in comparison to the piezoceramic side surfaces of the layers 30 smaller, they can be etched with less effort and thus parallel to the depth direction T in the multi-layer bar 10 reset to default.

Regardless of the previous production steps every second electrode 20 on the broadsides 12 electrically insulate, so that outer metallizations can be printed (step S7 in 11 ), the valleys become 40 filled with a slip. The slip fills the sinks 40 (see. 3 and 4 ) so far, that in each case in the sinks 40 arranged electrodes 20 covered by a layer (not shown). The slurry is preferably based on a ceramic or glassy powder, so that after drying the slurry an electrically insulating layer in the wells 40 over the electrodes 20 formed. During sintering S8 of the multilayer tie 10 the slip gets in the valleys 40 also solidified, so that a resistant layer formed without a separate heat treatment.

It is also preferred to use the multilayer bar 10 to process electrochemically after the sintering, ie to deposit conductive materials or side surfaces 22 ; 24 the electrodes 20 etched back to produce the sink structure described above. Below are the sinks 40 filled with slurry and this cured with a matched to him thermal treatment. Then the application of the outer metallizations and the separation of the multilayer bar into individual multilayer actuators takes place.

Before sintering S8 will be in the areas after the cutting of the multi-layer tie 10 individual multilayer actuators result, outer metallizations printed (S7). The printing of the outer metallizations is carried out for example by screen printing or other common methods. Subsequently, the multi-layer bar 10 sintered with outer metallization and into single multilayer actuators along the dashed lines in the 1A , B isolated. In the course of separation, the inactive areas 5 with the adjoining auxiliary electrodes 25 separated. It is preferable to perform the separation S7 after the sintering S8.

According to a further, not according to the invention, production alternative, the above-described sink structure by removing S5 of the side surfaces 22 ; 24 the electrodes 20 according to 5 to 10 generated. The production route with this method step S5 requires neither a multilayer bar 10 / Stack (see below) with auxiliary electrodes 25 and piezoelectrically inactive regions 5 another passivation layer. Therefore, a simplified processing compared to the previous process routes on a piezoelectric fully active layer structure is possible here.

In the multi-layer bar 10 in the green state, the in 5 shown in a section are on a broadside 12 the electrode surfaces 22 ablated. The ablation takes place by means of grinding, sawing, lasering, eroding and / or pushing in the depth direction T of the multilayer bar 10 , According to a first alternative of the removal S5 are on a broadside 12 the side surfaces 22 every second electrode 20 removed parallel to their course direction (cf. 5 . 6 ). The removal direction 60 is parallel to the side surface 22 aligned. Due to this editing, the side surfaces become 22 in the depth direction T in the multilayer bar 10 reset, leaving the sinks 40 arise. To illustrate shows 6 a section along the line AA 5 ,

The above process will be on both broadsides 12 of the multi-layer tie 10 to then sludge-isolate the wells, apply exterior metallizations, and perform S8 sintering (see above).

According to another alternative, the removal direction 60 not parallel to the direction of the side surfaces 22 ; 24 the electrodes 20 aligned (cf. 7 ). This opens up the possibility of only a portion of the side surfaces 22 ; 24 ablate to reduce the manufacturing cost. Looking at the section along the line AA in 7 , results from the non-parallel ablation again the sink structure (see. 8th ), as already described above. The valleys 40 are in this case spatially on a portion of the side surfaces 22 ; 24 limited, as from the cuts along the line BB and CC in 7 emerges (cf. 9 and 10 ). In this oblique removal compared to the direction of the side surfaces 22 ; 24 the electrodes 20 you will certainly the side surfaces 22 ; 24 cut and ablate in a partial area. This requires compared to the parallel removal of a lower adjustment effort of the machine for removal, each second electrode 20 in the multi-layer bar 10 reset and subsequently isolate.

After creating the sink structure on both broadsides 12 of the multi-layer tie 10 The same method steps and method alternatives are carried out as have already been described above.

It is also conceivable, the multi-layer bar 10 first to sintering and only then by ablation (see above) to create the sink structure. Subsequently, by means of slip in each case the side surface 22 ; 24 in the valleys 40 arranged electrodes 20 electrically isolated and the slurry solidified by thermal treatment.

According to an alternative, the removal is not performed on a multilayer bar, but already on a stack (not shown) of the future multilayer actuator. If the stack is in the green state, the thermal treatment of the slurry in the sink structure created by the removal is linked to the sintering of the stack. If the stack is in the sintered state, a thermal treatment for curing the slurry is carried out after the removal and application of the slurry in the sink structure.

Claims (3)

Manufacturing method for a piezoceramic multilayer actuator, comprising the following steps: a) producing a multilayer bar ( 10 ) as a green body consisting of an alternating arrangement of a plurality of piezoceramic layers ( 30 ) and a plurality of electrodes ( 20 ) in a stacking direction (S) of the multilayer bar ( 10 ), while a depth (T) of the multilayer bar ( 10 ) perpendicular to the stacking direction (S) of a depth of a multilayer actuator and a width (B) of the multilayer bar ( 10 ) perpendicular to the stacking direction (S) corresponds to a width of a plurality of multilayer actuators, wherein the electrodes ( 20 ) over the entire depth (T) of the multilayer bar ( 10 ) so that all side surfaces ( 22 . 24 ) of the electrodes ( 20 ) each to the surface of broadsides ( 12 ) of the multilayer bar ( 10 ) and where the electrodes ( 20 ) alternately on opposite end faces ( 15 ) of the multilayer bar ( 10 ) starting from not the full width (B) of the multilayer bar ( 10 b) arranging opposing auxiliary electrodes ( 25 ) to the width (B) of the multi-layer bar ( 10 ) spaced end faces ( 15 ), so that with the opposite auxiliary electrodes ( 25 ) around an electrode ( 20 ) in the stacking direction (S) each offset every second electrode ( 20 ) is electrically controllable, c) electrochemical resetting parallel to the depth (T) of the multilayer bar ( 10 ) by etching a side surface ( 22 ; 24 ) every second electrode ( 20 ), so that on opposite broad sides ( 12 ) of the multilayer bar ( 10 ) each second side surface ( 22 ; 24 ) of the electrodes ( 20 ) in the multilayer bar ( 10 ) and the recessed side surfaces ( 22 ; 24 ) of the electrodes ( 20 ) on opposite broad sides ( 12 ) of the multilayer bar ( 10 ) in the stacking direction (S) around a piezoceramic layer ( 30 ) are spaced apart from each other, d) coating the recessed side surfaces ( 22 ; 24 ) of the electrodes ( 20 ) with an electrically insulating layer and applying in each case a plurality of outer electrodes on the opposite broad sides ( 12 ) of the multilayer bar ( 10 ) parallel to the stacking direction (S), e) sintering and separating the multilayer bar ( 10 ) parallel to its depths (T) and stacking direction (S) in a plurality of piezoceramic multilayer actuators, wherein after sintering the end faces ( 15 ) with the auxiliary electrodes ( 25 ) are separated such that no piezoelectrically inactive regions ( 5 ) in the multilayer bar ( 10 ) remain behind. Manufacturing method according to claim 1, in which the recessed side surfaces ( 22 ; 24 ) of the electrodes ( 20 ) each in a sink ( 40 ), which are filled and burned for coating with an electrically insulating layer of a ceramic or glassy slip casting. A manufacturing method according to claim 1 or 2, in which the plurality of external electrodes are provided on opposite broad sides ( 12 ) of the multilayer bar ( 10 ) are printed.

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